July 2, 2001 -- For some women facing the change of life, soy products may be nature's answer to coping with the hormonal swings that can wreak havoc as estrogen levels drop. Like estrogens, natural chemicals found in the soybean, called phytoestrogens, can reduce menopausal symptoms.
Better yet, they may protect the heart by lowering "bad" cholesterol without increasing blood clotting, according to research presented recently at the Endo 2001 meeting in Denver. And although estrogen is classically thought of as a female hormone, soy may also benefit men.
"This research is interesting as it suggests soy can favorably affect cholesterol without adversely affecting blood clotting, which is a potential concern with estrogen replacement," Len Kritharides, PhD, FRACP, tells WebMD after reviewing the findings. He is a cardiologist at Concord Hospital, and leader of the Heart Research Group at the University of Sydney in Australia.
After menopause, loss of estrogen makes women more vulnerable to heart disease. By lowering "bad" cholesterol, estrogen replacement therapy prevents build up of plaque in the arteries. But that helpful effect may be wiped out by estrogen's tendency to increase blood clotting, which can cause heart attack and stroke.
In more than 100 men and more than 100 women after menopause, those who took a daily supplement of soy protein containing phytoestrogens had a drop in blood pressure and in "bad" cholesterol and blood fats relative to those who did not.
"The benefits were seen equally in men and women, [and] soy treatment did not affect male sexuality," researcher Helena J. Teede, MD, tells WebMD. Ingredients in soy that protect the heart may not work by affecting estrogen, explains Teede, a senior lecturer in medicine and an endocrinologist at Monash University in Melbourne, Australia.
In addition, "soy containing phytoestrogens did not affect blood clotting processes ... which contribute to the adverse effects of estrogen hormone replacement therapy," researcher Barry McGrath, MD, a professor of vascular medicine at Monash, tells WebMD.
"The major problem with soy is the contention that it lowers cholesterol," says Barry R. Goldin, PhD, a professor of nutrition at Tufts University School of Medicine in Boston. He explains that previous studies have shown only a modest effect on lowering cholesterol by 0-5%.
"For individuals who require cholesterol lowering because of total cholesterol above 240, I believe it is a medical error to withhold effective cholesterol lowering drugs and use soy as a treatment," Goldin tells WebMD.
Part of the discrepancy in results from different studies may reflect use of different soy products. As is so often the case with nature, the perfect package growing on the vine may have healing powers difficult to duplicate in the laboratory.
In at least two studies, pills made from soy extracts did not improve blood cholesterol, according to Thomas B. Clarkson, DVM, a professor of comparative medicine at the Wake Forest University School of Medicine in Winston-Salem, N.C. He tells WebMD that different proteins found in natural soy appear to interact with phytoestrogens to increase their cholesterol-lowering activity.
"We are conducting further research into the active components of soy and their mechanisms of action, and are also examining whether soy protein can be an effective addition to treatment in patients at high risk of [heart] disease, such as those with [high blood pressure] or diabetes," McGrath says.